The present invention relates to a method and a device for detecting, in a return signal, the presence of components other than echo components from a forward signal. It finds a particular but not exclusive application in the field of adaptive echo cancellers.
Echo cancellers are used in bidirectional links. Their purpose is to cancel, or at least substantially to attenuate, in the signal flowing in one of the two directions (the return signal) the echo components from the signal flowing in the other direction (the forward signal) appearing in the region of the reception site of the forward signal. The echoes may be of acoustic origin, for example in the application to hands-free telephone instruments, or of electrical origin. The echo canceller usually includes a filter which models the echo paths in the region of the reception site of the forward signal. This filter receives the forward signal, and its output, which is an estimate of the echo components, is subtracted from the return signal.
In an adaptive echo canceller, the coefficients of the modeling filter are adapted in real time in order to minimize the energy of the residual return signal. When the return signal contains useful components and not only echo components from the forward signal, it is appropriate to fix the procedure of adapting the coefficients in order to avoid degrading the useful components and in order not to cause undesirable oscillations or divergences in the values of the coefficients.
However, the detection in the return signal of the presence of useful components other than the echo components from the forward signal proves to be a difficult problem. It is certainly possible to envisage calculations of correlations between the forward and return signals on the basis of which the detection could be performed. However, such a method implies considerable volumes of calculations, currently incompatible with practical applications.
An object of the present invention is to afford a solution to the above problem, which is realistic in terms of volume of calculations.